On Thu, 8 Sep 2005, Jim Ramsay wrote:
> More information:
>
> The error only occurrs during device sensing when the
> srb->request_buffer is assigned as follows, by usb/storage/transport.c
> in the routine usb_stor_invoke_transport:
>
> old_request_buffer = srb->request_buffer;
> srb->request_buffer = srb->sense_buffer;
>
> Now, this is a problem because srb->sense_buffer is defined as follows
> in the struct scsi_cmnd:
>
> #define SCSI_SENSE_BUFFERSIZE 96
> unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE];
>
> Since it is not allocated at runtime there is NO WAY the SCSI layer
> can possibly guarantee it is page- or cache-aligned and ready for DMA.
>
> Any suggestions on best fix for this? Is it still a SCSI-layer issue?
> Or should USB step up in this case and ensure this buffer is dma-safe
> itself?
Aha!
I've long thought that usb-storage should allocate its own transfer buffer
for sense data. In the past people have said, "No, don't bother, it's not
really needed." Here's a good reason for doing it.
Expect a patch before long.
Alan Stern
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